[Tony Gilbert]

Posted 8.45pm Mon

Slight Risk of Thundery Showers 09Z-20Z Eastern half of Ireland, Central & Northern UK as per map Tues 10th July

Slight Risk of Funnel Cloud Development

Confidence level; Low

A complex outlook with several weak frontal boundaries connected to a stationary surface low over the UK. Long wave upper trough extends to primarily effect Ireland but with only marginal influence across the UK. Upper shear values and PV rather weak for both UK & Ireland.

ATM a rather low end outlook so I will keep the detail brief for now; Both GFS and WRF break out convective showers quite early in the period across central UK regions. Some good potential for insolation by mid day onwards and could well turn some of these thundery. A very moist boundary layer with a good ratio for dew points to surface temps should develop some fairly low cloud bases. Models suggest a hard convergence zone running from just west of the Wash up to western Scotland. Much of the initial convective development will likely trigger along this zone. A higher resolution look at the surface flow looks to develop an optimum confluent vector where strong horizontal shear can develop. This low level vorticity can easily be stretched upward into any passing updraft and hence a risk of funnel clouds. Having said that I do not see the outlook comparable to a classic funnel day; The atmosphere looks saturated up to the tropapause and this will likely reduce buoyancy above the LFC and hence might impede updrafts. It is also noted that any instability across the UK will be tied directly into surface heating. The strongest lapse rates will therefore occur close to the ground whereas we are likely to see relatively weak lapse rates aloft.

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This post has been edited by Tony Gilbert: 09 July 2012 - 20:14

[Flatlander]

Thanks Tony. We had a persistent convergence line today and I'm slightly surprised there weren't any funnel reports.

Probably everyone was too busy watching the rain...

[Tony Gilbert]

UPDATE 8.20am Tues

As per earlier forecast with moderate risk of Tstorms Western Regions Ireland. Experiment box (yellow) added to UK zone for best risk of FC's.

Confidence Level; LOW

GFS takes a sharp downturn in the potential for Tstorms over UK whereas WRF increases risk. Forecast remains warranted at a low confidence level based solely on the WRF ATM. Nevertheless the overall picture looks at best to suggest isolated pockets of convection today Midlands through to Humber and a zone around Swindon later in period. Regions less conducive now include northern England & Scotland where heavy cloud over surface occlusion looks fairly non convective now.

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